Bought an Abacus yesterday. I had some eagerness to know how a simple mechanical instrument does all the complicated caluclations. As it turns out in a short span of time I was able to do some simple additions and subtractions and believe me it was loads of fun. If u wanna know more Click here and don't be surprised when i tell u that it has been voted as the second most valuable tool of all time by forbes My Abacus